Design and Evaluation of a Pilot-Scale Permeable Reactive Barrier System for Nitrate Load Reduction in Agricultural Surface Runoff Water

Abstract

The need to increase food security has led to the over-application of synthetic fertilizers. Nitrate is a highly mobile fertilizer in soils, so when it comes into contact with a body of water, it can initiate a process of eutrophication by over-enriching it, as well as cause a disease known as methemoglobinemia. The objective of the present research was to design and evaluate a permeable reactive barrier to remove nitrates in agricultural surface runoff water. This research has a pilot type scope, at laboratory scale and applied since the results will solve an identified problem, of exploratory cut from the point of view of the depth of the research, because it deals with a new field in Nicaragua. For this purpose, two permeable reactive barriers were built with dimensions of 1.0-meter-long, 0.5 m wide and 0.5 m deep, profiled in CIRA/UNAN-Managua. The first was filled with soil from the site, the second with a mixture of soil plus a substrate (previously selected). The system was fed with a mixture of 100 mg/l of nitrates from a commercial synthetic fertilizer (FORMUNICA, NH4NO3). As a carbon source, sawdust was used for the development of denitrifying bacteria. Samples were taken at the outlet of the system on days 0, 7, 9, 12, 15 and 19, for subsequent analysis of the nitrates present. The removal efficiency of the system was 55% for the control bed and 66% for the denitrifying bed. It is important to highlight the findings related to the operation of the Barriers from the physical point of view, since this technology is a low-cost alternative, easy to build, maintain and manage, with efficient results for nitrate removal.